Investigation of heat-treated artefacts from Pleistocene sites

Abstract

The paper presents an overview of the current state of investigation of heated and heat-treated artefacts from Pleistocene sites, the methods frequently used in such investigation, and the main goals of similar research. Heated artefacts should be targeted in pre-excavation (mostly by non-destructive surficial methods), excavation (e.g., primary visual estimation, archaeomagnetic measurements in situ), and the post-excavation phases (a range of analytical methods). Apart from distinguishing heated artefacts, we are frequently able to date them directly, distinguish deliberately heated artefacts, assess the role of heat treatment on different Pleistocene sites, and draw conclusions about the spatial organization of such sites based on the distribution of heated artefacts. Successful heat treatment made stone knapping easier, enabled pressure flaking and the formation of sharper edges. The main causes of such improvements are the closing of pores due to the formation of new bonds, the appearance of fluid inclusions with high-velocity crack propagation, and potentially neo-formed iron oxides or other fluxes in the siliceous matrix. In view of recent research, the recrystallization of silica matter or the positive role of microcracks within the siliceous matrix are less probable causes of improved flakeability. Heat treatment was a type of technological and symbolic adaptation of modern humans to the frequently hostile environments of the Pleistocene as the two spread together over the world before the onset of the Holocene. The oldest dates of the technique currently come from the Near East. Though it might have spread from there to some parts of Eurasia, polycentric invention of heat treatment in the Pleistocene must be assumed. Independent centres of development of the technique are probably southern Africa, South America or Australia – relatively isolated regions where technological influence from other areas is not evidenced.